POPULATION-DYNAMICS OF COMMON SANDPIPERS ACTITIS-HYPOLEUCOS BREEDING ALONG AN UPLAND RIVER SYSTEM

The survival rate of a colour-ringed Common Sandpiper population followed from 1977 to 1989 averaged 0.79 per year, but fluctuated in response to April weather. Late April snowstorms in 1981 and 1989 reduced the apparent survival rates, from the previous years, to 0.39 and 0.50, respectively, and the breeding populations fell from 21 to 14 and from 20 to 12 pairs. Recovery from the reduced population size in 1981 proceeded slowly, at increments of only 1 or 2 pairs per year. There appears to be a low rate of recruitment in this population, sufficient to balance the low mortality rate in average years but inadequate to compensate for the extreme mortality produced by extreme weather.